I did a bit of digging. Technically Frum is correct, however Congress basically ceded a lot of the tariff laws to the executive branch. Going back to Smoot Hawley in the 1930s, and other tariff acts in the '60s and 70s, Congress has given the President the power to impose and negotiate tariffs.
If you take the originalist's view Trump has overstepped his boundaries. The history of the courts says otherwise, they gave up that power a while ago.
Or at least that's what ChatGPT tells me
And since we have long agreed that this Congress has given up basically all designs at actual governing....and the Supreme Court has turned itself into a pretzel.....